This invention relates to methods of and a device for measuring the curvature of an object and particularly relates to methods of and a device for measuring the curvature of shafts such as, for example, shafts of golf clubs.
Frequently, it is important to determine the curvature of objects in a static condition or in a dynamic condition to obtain data representative of, or to determine, characteristics of the object when the object is placed in a use environment. For example, in the sporting industry, such objects could include golf club shafts, fishing rods, fencing foils, archer's bows and the like. Also, in other industries, such as the construction industry or the space industry, many examples can be found where data relating to the static or dynamic curvature of an object would be valuable and necessary.
In the past, several techniques have been used to determine the curvature of objects. In some instances, strain gage devices have been used wherein incremental characteristics of wires of such devices change in response to the corresponding incremental curvature of the object being measured and such changes are determined as an indication of the curvature. Strain gage devices of this nature are noted in U.S. Pat. No. 3,991,745 which issued on Nov. 16, 1976.
In another technique which is employed to determine the curvature of objects, one end of a golf club shaft is mounted in a support with the remainder of the shaft extending in a cantilever fashion from the support. A weight is attached to the shaft at a location spaced from the support to cause the shaft to curve downwardly. Various measurements are taken and the shaft deflection, which is related to the slope of the bending angle of the shaft, is determined. The weight may be selectively placed at a variety of locations along the length of the shaft and a range of deflections may be determined. A process of this type is disclosed in U.S. Pat. No. 4,558,863 which issued on Dec. 17, 1985.
In the sport of golfing, it is advantageous for the golfer to use a matched set of clubs wherein the shaft of each club has characteristics which match the corresponding characteristics of the remaining clubs of the set. In many instances, golfers become accustomed to a personalized set of clubs wherein the feel and performance of the clubs enhances the golfer's playing of the game. When a golfer plans to use a new or different set of clubs, it is to the golfer's advantage to use clubs which have the same feel and performance of the older clubs to provide consistency in the golfer's game.
One technique for matching clubs is disclosed in U.S. Pat. No. 5,163,681 which issued on Nov. 17, 1992, wherein the butt end of the shaft of the club is mounted in a support and a dummy club head is mounted on the opposite cantilevered end of the shaft. The shaft is then oscillated over a range of frequencies by use of an oscillating means associated with the support. The excursion of the head from a stationary position is measured at each frequency and is plotted against the frequency of the head to form a curve which is defined as the "spectral response curve." By use of this data, matching clubs may be selected.
While the techniques described above provide data within the capability and complexity of the facilities used with such techniques, there remains a need for a device which will measure the incremental curvature of an object in a simple and comprehensive manner. In addition, there is a need for a device which will measure incrementally the curvature of a shaft along its natural curving axis even though the exterior of the shaft may not be of a consistent diameter from one end of the shaft to the other end. In particular, there is a need for a device for measuring the curvature of a shaft along its curving axis even though the shaft is tapered from one end to the other end.